LITHIUM-ION BATTERY

April 28, 2013

For many years, nickel-cadmium had been the only suitable battery for portable equipment from wireless communications to mobile computing. Nickel-metal-hydride and lithium-ion emerged in the early 1990s, fighting nose-to-nose to gain customer’s acceptance. Today, lithium-ion is the fastest growing and most promising battery chemistry.

The lithium-ion battery

Pioneer work with the lithium battery began in 1912 under G.N. Lewis but it was not until the early 1970s when the first non-rechargeable lithium batteries became commercially available. Lithium is the lightest of all metals, has the greatest electrochemical potential and provides the largest energy density for weight.

Attempts to develop rechargeable lithium batteries failed due to safety problems. Because of the inherent instability of lithium metal, especially during charging, research shifted to a non-metallic lithium battery using lithium ions. Although slightly lower in energy density than lithium metal, lithium-ion is safe, provided certain precautions are met when charging and discharging. In 1991, the Sony Corporation commercialized the first lithium-ion battery. Other manufacturers followed suit.

The energy density of lithium-ion is typically twice that of the standard nickel-cadmium. There is potential for higher energy densities. The load characteristics are reasonably good and behave similarly to nickel-cadmium in terms of discharge. The high cell voltage of 3.6 volts allows battery pack designs with only one cell. Most of today’s mobile phones run on a single cell. A nickel-based pack would require three 1.2-volt cells connected in series.

Lithium-ion is a low maintenance battery, an advantage that most other chemistries cannot claim. There is no memory and no scheduled cycling is required to prolong the battery’s life. In addition, the self-discharge is less than half compared to nickel-cadmium, making lithium-ion well suited for modern fuel gauge applications. Lithium-ion cells cause little harm when disposed.

Despite its overall advantages, lithium-ion has its drawbacks. It is fragile and requires a protection circuit to maintain safe operation. Built into each pack, the protection circuit limits the peak voltage of each cell during charge and prevents the cell voltage from dropping too low on discharge. In addition, the cell temperature is monitored to prevent temperature extremes. The maximum charge and discharge current on most packs are is limited to between 1C and 2C. With these precautions in place, the possibility of metallic lithium plating occurring due to overcharge is virtually eliminated.

Aging is a concern with most lithium-ion batteries and many manufacturers remain silent about this issue. Some capacity deterioration is noticeable after one year, whether the battery is in use or not. The battery frequently fails after two or three years. It should be noted that other chemistries also have age-related degenerative effects. This is especially true for nickel-metal-hydride if exposed to high ambient temperatures. At the same time, lithium-ion packs are known to have served for five years in some applications.

Manufacturers are constantly improving lithium-ion. New and enhanced chemical combinations are introduced every six months or so. With such rapid progress, it is difficult to assess how well the revised battery will age.

Storage in a cool place slows the aging process of lithium-ion (and other chemistries). Manufacturers recommend storage temperatures of 15°C (59°F). In addition, the battery should be partially charged during storage. The manufacturer recommends a 40% charge.

The most economical lithium-ion battery in terms of cost-to-energy ratio is the cylindrical 18650 (size is 18mm x 65.2mm). This cell is used for mobile computing and other applications that do not demand ultra-thin geometry. If a slim pack is required, the prismatic lithium-ion cell is the best choice. These cells come at a higher cost in terms of stored energy.

Advantages

High energy density – potential for yet higher capacities.

Does not need prolonged priming when new. One regular charge is all that’s needed.

Relatively low self-discharge – self-discharge is less than half that of nickel-based batteries.

Low Maintenance – no periodic discharge is needed; there is no memory.

Specialty cells can provide very high current to applications such as power tools.

Limitations

Requires protection circuit to maintain voltage and current within safe limits.

Subject to aging, even if not in use – storage in a cool place at 40% charge reduces the aging effect.

Transportation restrictions – shipment of larger quantities may be subject to regulatory control. This restriction does not apply to personal carry-on batteries.

Expensive to manufacture – about 40 percent higher in cost than nickel-cadmium.

Not fully mature – metals and chemicals are changing on a continuing basis.

Graphics for the slide presentation that follows were furnished by Charles Murray, Senior Technical Editor for “Design News”.

Let’s take a tour through existing uses for lithium-ion battery technology to see what technology is currently being applied.

Engineers of Nissan’s Leaf, which made its debut in 2010, wanted their car to have a battery that wouldn’t lessen valuable rear-seat space. Instead of placing the lithium-ion batteries in the back seat and trunk, they created a 24-kWh pack that resides under the floor. You can see that application with the JPEG given below. The issue I have with this design is maintenance and possible replacement. You must be able to get to the assembly without excessive time for repairs and replacement. (Source: Nissan)

The Leaf’s 480-lb battery pack is made up of 48 stackable lithium-ion modules. This is considerable weight and probably means a reduction in weight for other structures. Composite materials which are lighter but just as strong as steel are being used for total weight reduction. (Source: Nissan)

In 2011, Apple’s MacBook Air used lithium polymer batteries to achieve its 0.67-inch thickness. As you can see, the profile is very thin with smooth-flowing lines, only made possible by the Li-Ion battery pack. (Source: Apple)

We’ve looked at the Leaf; now let’s take a look at the Chevy Volt battery system. The Chevy Volt, which reached production late in 2010, uses a familiar T-shaped battery pack that stores about 16 kWh of energy. (Source: GM)

GM engineers beefed up the battery safety cage to help the Volt resist the kinds of forces seen in NHTSA’s side pole crash test, added a new sensor to monitor coolant levels, and placed a tamper-resistant bracket atop the coolant reservoir.

Introduced in October 2011, Boeing’s 787 Dreamliner was among the first to employ lithium-ion batteries for auxiliary power back-up. In the past, commercial airliners had typically used nickel-cadmium chemistries. A fire in a Dreamliner parked at Boston’s Logan Airport drew attention to Boeing’s lithium-ion batteries in January 2013. Using data from the Boeing 787 flight recorder, National Transportation Safety Board investigators determined that the cause of the lithium-ion battery fire was short circuit in one of the battery’s eight cells, which led to a thermal runaway condition. (Source: NTSB)

More traditional batteries are made by Panasonic. In 2011, Panasonic introduced its NCR18650A lithium-ion batteries. Offering a capacity of 3.1 A-h, the batteries were targeted at handheld devices. (Source: Panasonic)

Ford’s five-passenger Focus Electric, which reached production in 2012, employs a 23-kWh lithium-ion battery pack. Using a fast-charging scheme, it can be recharged in three to four hours at 240V. (Source: Ford Motor)

In 2012, start-up Envia Systems said they created a lithium-ion battery that offers three times as much energy as conventional lithium-ion, at half the cost. (Source: Envia Systems)

In 2008, Tesla Motors introduced its all-electric two-seat Roadster, which used more than 6,800 lithium-ion cells in an aluminum-enclosed 990-lb package. Inside the pack, cells were organized into 11 modules, with each containing their own control board and microprocessor. Total capacity of the battery was 53 kWh. (Source: Tesla Motors)

This has been a very quick slide show but will demonstrate why Lithium-Ion technology is important and probably will be with us for the foreseeable future. I definitely will keep you updated relative to this important field of science. Hope you enjoyed the posting and I certainly look forward to your comments.

8 Responses to “LITHIUM-ION BATTERY”

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